In an apparatus or system for the development of aluminium lithographic printing plates of the type disclosed in EP 410500 it is advantageous to maintain the strength of the processing liquids within specified limits so as to maintain high quality printing plates, and reduce waste products.
During processing the photographic sheet material it is an advantage if the carry-over from one chemical bath to another chemical bath is kept to a minimum. It is therefore known to use pairs of squeeze rollers at the exit of a chemical bath to remove excess chemicals from the sheet material as it exits the bath.
A good removal of processing liquid is also required to reduce the drying time of the sheet material after the last process bath, and hence reduce energy use.
In order to obtain good imaging quality it is necessary for the rollers to exert a load in the order of 0.5-6.0 N/cm roller length to remove excess materials. To this end the rollers are biased together typically by springs which act on the ends of the roller shafts.
During the processing of the photographic material the roller can become coated with gelatin and if the apparatus is switched off with the rollers stationary and biased together then after several hours the rollers become glued together by the gelatin. As a result of this the roller surfaces may become damaged, and the drive gears may also be damaged when the apparatus is restarted.
Furthermore since the rollers have an elastomeric surface, if the apparatus is left with the squeeze rollers biased together, the rollers may take on a set and become temporarily deformed and when the apparatus is restarted this may result in poor quality image reproduction for the first few plates processed on the re-start, after which until the deformation disappears.
There are known mechanisms which can lift the rollers of a pair of squeeze rollers from each other in order to overcome the described problems. One suitable mechanism is disclosed in EP A10 177 873. This mechanism comprises U-like sliding beams extending past a plurality of roller pairs and the legs of which are provided with staggered openings with sloping edges. Depending on the longitudinal position of the beams, bearings of the rollers are either seated on the upper or lower legs of the beams so that the rollers are correspondingly biased towards each other, or are opened. This mechanism requires an in-line mounting of the several roller pairs, it excludes an individual removal of a roller pair for servicing or the like, and an activator must be provided for controlling the position of the beams.